BY W. G. W00LN0UGH AND T. G. TAYLOR. 551 



of the leaves on its terminal branches. It is met with, so far as 

 our experience goes, chiefly, if not entirely, on the gravels of the 

 Wollondilly. It rarely, if ever, transgresses the limits of this 

 formation, and is not found on the sandstone, quartzite, granite, 

 &c, upon which the gravels rest. All along the course of the 

 old gravels, from Digger's Creek at least, as far as the railway 

 line, this tree is very conspicuous. This fact may serve as 

 additional evidence of the relationship of the area under con- 

 sideration to the Wollondilly system. 



Physiographical History of the District. — At some period, 

 geologically comparatively recent, this area underwent extensive 

 base-levelling. A number of geological formations occur, 

 probably unequalled for variety in any other district of equal 

 size in the State. These include Silurian slates, jaspers, quartzites, 

 and limestones, Permo-Carboniferous marine and fresh-water 

 beds, Triassic sandstones and conglomerates, together with pre- 

 Permo-Carboniferous granites and quartz-porphyries, and Caino- 

 zoic basalts and tuffs (1). These formations were reduced to the 

 character of a peneplain. An elevation of 400 to 500 feet then 

 took place which revived the streams. During a long period of 

 stable equilibrium the rivers again cut down almost to base-level. 

 The chief streams flowed parallel to one another in a general 

 S.S.W. to N.N.E. direction, through a low-lying plain. A grand 

 elevation of 2000 feet now followed, raising the low-level plain 

 into a plateau. River-action again became very active, and deep 

 canons were begun. Short, steep, coastal streams by reason of 

 their rapid flow incised their channels and formed narrow, 

 V-shaped canons, cut down almost to sea-level. The heads of 

 these valleys worked backwards rapidly. One such stream 

 occupied the position of the present Lower Shoalhaven. 

 Working back westerly, it was at last able to tap the waters of 

 the old N. and S. river and capture the upper part of its valley, 

 thus producing the present stream-distribution. This last phase 

 is of very recent date, as is shown by the fact that the present 

 valley of the Shoalhaven is a beautifully typical young river 

 valley, its cross section being an absolute V- The capture has 



